1. Field of the Invention
The present invention relates to an electronic control device for an ignition timing in a fuel injection type internal combustion engine.
2. Description of the Related Arts
In an electronic controlled fuel injection engine, fuel injections from injectors provided at each cylinder of the engine are basically carried out at predetermined timings in one cycle of the operation of the engine. Such fuel injections are therefore called synchronous injections, and are made in an amount which is determined so that a desired air-fuel ratio is obtained at a steady state condition of the engine in which the degree of the depression of a throttle valve remains substantially unchanged. Nevertheless, the amount of fuel determined by the synchronous injections becomes less than that required to obtain the desired air fuel when the engine is under an acceleration condition, and therefore, conventionally, an acceleration fuel enrichment correction is carried out to obtain a desired air-fuel ratio when the engine enters an acceleration condition. Such an acceleration fuel enrichment correction is obtained by asynchronous fuel injections, which are carried out immediately upon the detection of an acceleration. The asynchronous injection is carried out regardless of the timing in one cycle of the engine operation, and this is completely different from the synchronous injections which are carried out at predetermined timings in one cycle of the engine operation.
The asynchronous injection is used to obtain a desired air-fuel ratio during the acceleration condition so that a sufficient torque that will maintain a necessary acceleration performance is obtained. Such an asynchronous fuel injection, however, causes a too rapid increase in the engine torque, which causes a driver to feel an acceleration shock and the vehicle to be subjected to an undesirable back and forth movement, which adversely affect the driveability of the vehicle.
Therefore, it has been proposed, in addition to the asynchronous fuel injections upon the detection the acceleration condition, to control an ignition timing so that it is delayed with respect to an optimum timing for obtaining the maximum torque, and as a result of such a delay of the ignition timing, the rapid increase in the engine torque is suitably suppressed and a desired driveability is maintained.
In this prior art, a predetermined fixed amount of delay is applied only to the ignition timing when an acceleration condition is detected, regardless of the degree of acceleration. The acceleration is detected as a predetermined value of a change in a value of an intake pressure per unit of time, or by a throttle switch for detecting that a degree of opening of the throttle valve is larger than a predetermined value. Nevertheless, such a fixed amount of a retarding of the ignition timing, when determined to match a rapid acceleration, causes misfires during a mild acceleration, since the ignition timing is too far delayed. To avoid this disadvantage, it is possible to select a small value of the amount by which the ignition timing is retarded, but this has a drawback in that an acceleration shock is generated when the engine is under a rapid acceleration, since the delay in the ignition timing is too small, and thus the driveability is worsened.